Air assisted fuel injectors for automotive internal combustion engines take advantage of the natural air flow in an engine, due to manifold vacuum, to better atomize fuel spray, which, in turn, is known to improve combustion and efficiently reduce exhaust emissions. Typically, the engine includes an assist air passage which communicates with the fuel injector for providing assist air to the nozzle of the fuel injector for atomization. It is also known to use fuel injectors which target the fuel spray within the engine. However, assist air in such air assisted fuel injectors tends to disrupt any spray targeting which may be performed by the fuel injector.
European Patent Application #EP740,069 ('069) shows an air assisted fuel injector having an air shroud placed on the nozzle of the injector. Assist air is directed to the fuel spray as it emerges from the fuel injector nozzle for fuel atomization. Also, director holes are formed in the shroud for targeting the atomized fuel spray. According to '069, air is injected in the liquid fuel stream at the same location where fuel targeting is performed. Because the atomized fuel is contained within director holes, targeting may be maintained.
The inventor of the present invention has found certain disadvantages with prior art air assisted fuel injectors that attempt to maintain targeting. For example, with respect to '069, the gallery where assist air atomizes the fuel spray is relatively restricted. This restriction may adversely effect fuel flow from the fuel injector due to back pressure variability downstream of the fuel nozzle.
In addition, the shroud of the '069 patent requires that an air port be formed in the engine's cylinder head or intake manifold close to the fuel discharge point to feed assist air to the shroud. This is inconvenient due to the proximity of the fuel discharge point to the intake valve of the engine.